1. Technical Field
One or more embodiments of the present invention generally relate to a system and method for hydrating a proton exchange membrane fuel cell (PEMFC).
2. Background Art
It is known that a number of fuel cells are joined together to form a fuel cell stack. Such a stack generally provides electrical current in response to electrochemically converting hydrogen and oxygen into water. The electrical current generated in such a process is used to drive various devices in a vehicle or other such apparatus.
Each fuel cell within the stack generally includes first and second flow plates, an anode, a cathode, and the PEM (or membrane). The anode and cathode each include a catalyst. The first and the second flow plates define flow fields for facilitating hydrogen and oxygen flow (e.g., or air) through the anode and the cathode, respectively. The anode, the catalyst, the membrane, and the cathode are generally sandwiched between the first and the second flow plates. Hydrogen is channeled through the flow field of the first flow plate to the anode of the fuel cell. Oxygen is channeled through the flow field of the second flow plate to the cathode of the fuel cell. The anode catalyst causes the hydrogen at the anode to split into positive ions and electrons. The membrane allows the positive ions to pass through to the cathode while the electrons travel along an external circuit to the cathode. Such a travel of the electronsalong the external circuit to the cathode generates electrical current. At the cathode, the positive ions and the electrons combine with the oxygen to form water that is discharged from the fuel cell.
In general, the hydration state of the membrane is a parameter that influences fuel cell performance. There should be an adequate amount of water in the membrane of each fuel cell to avoid degradation and to lower membrane resistance to meet performance needs.
The water in the membrane may come from two sources. A first source of water may come from the incoming humidified hydrogen and/or air that is passed through the anode and/or cathode, respectively. Optionally, water may come from humidified air that is passed through the cathode. A second source of water is generated by the oxygen reduction reaction on the cathode. To generate wet gases, a certain amount of parasitic power may be needed. Parasitic power is a part of the gross stack power that is needed to run a balance of plant components, such as pumps, humidifiers or other suitable devices. To minimize the parasitic power, drier gas may be preferred. In some cases, newly developed membranes may operate with a much drier gas (e.g., under 50% of relative humidity) at the inlet of the fuel cell stack. When the fuel cell stack operates at low loads (e.g., low current generating mode or when the vehicle is in an idle state), the cathode reaction is low and the amount of water generated may not be sufficient to hydrate the membrane.